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What The Waterproof K Ratings Really Mean:
It can be pretty bewildering when it comes to choosing your ski jacket or snow pants. There’s tons to choose from, and a huge array of brand names dreamed up by a combination of inventors and marketing departments. This huge volume of names, numbers ,and letters, is enough to confuse anyone!
But don’t worry, the team at Snowtrax are here to shine a light on what’s going on under the surface of your next jacket.
First of all, what’s the difference between a membrane and a sealed fabric?
You may see these terms on the ticket of the outerwear, generally followed by a diagram showing droplets fleeing from the fabrics. But, there is an important difference.
In it’s simplest terms a sealed fabric is an impermeable layer created by either using a plastic sheet, or sealing a woven fabric inside a waterproof material. Originally conceived by fishermen and later know as oilskins, they used canvas and coated it in an oil based rubber that set and made the material waterproof (highly waterproof but not very flexible).
Modern materials and techniques have improved hugely but the idea remains the same. The biggest drawback of a sealed garment is that while water can’t get in, water vapour and sweat also can’t get out. This means that without careful design and ventilation these garments can end up leaving you feeling rather sweaty and damp even if the snow/rain never made it through. A good example of this would be the kind of emergency ponchos that are made of a very thin plastic. They do keep the rain out, but quickly start feeling clammy and damp from your own body heat.
Membrane garments (like Gore-Tex and all the other brands variations) work using a thin sheet of PET or ePTFE that is peppered with millions of holes that are too small for water droplets to get through but big enough for water vapour to escape. This thin sheet (membrane) is then attached to a hard wearing, woven, outer shell of fabric that is coated in a Durable Water Repellent chemical that stops the outer layer saturating.
DWR coating making water droplets bead up instead of saturate the material.
The advantage is that while water is stopped from getting in all your sweaty humid air can get out! But as with any material, water can get forced through if enough pressure is used (A part of the first K measurement).
What about those “K” numbers?
More often than not, outerwear is rated with something like 15K/10K. Sounds complicated but actually it’s just a measurement of it’s water resistance vs it’s breathability. Known as the "Hydrostatic Head", the water resistance is calculated by putting an inch square tube on the material and seeing how tall a water column (measured in thousand mm) the material can support before any leaks appear.
A material that can support a 20 meter water column is rated 20K waterproof.
Although it’s unlikely that you’ll put your fabric under 20 meters of water, the part that matters here is the potential for the fabric to resist water under pressure. If you’re sitting on a wet seat in your snow pants the water may only be 1mm deep, but the pressure exerted by your body weight could be enough to force it through lower rated fabrics.
Breathability is the second “K” number and this is measured in Grams of water per square meter per day. In other words, it measures how much vapour can pass through a square meter of fabric within 24 hours. So, based on how much you think the activity is likely to make you get hot and sweat you may want to look for a higher breathability. This is very important in cold climates!
It may be frozen, but there's a lot of water in this photo!
So, what does this mean for you and your skiing or snowboarding?
It’s probably easier to think of the ratings in low, medium, or high. With low being anything below 10K, medium being 10 to 20K, and high being 20K+. The same scale applies for the breathability side of things. So for a water resistant jacket that just needs to cope with a quick shower between the bar and the chalet it’s going to be fine at 8K. Where as a outerwear designed to deal with heavy downpours, wet snow, or being pressed into snow repeatedly you would need something over 10K and preferably 15K-20K+ if you think you’re going to be rubbing snow into the surface.
When it comes to breathability it’s particularly important if you’re going to be in the cold as damp clothing will quickly freeze when you stop moving, leaving you at a much higher risk of hypothermia and exposure. Backcountry ski touring for instance requires a lot of exertion on the way up which results in sweating but then at the top of the run you have to stop to transition ready for the downhill section and this is where the sudden decrease in temperature can happen. The reason is that water strips heat away from the body about 25 times faster than air of the same temperature!! Better breathability gets rid of more water vapour and makes for a drier and warmer jacket on the inside!
Skinning up creates lots of heat but highly breathable materials can manage the temperature well.
So that’s the fabrics dealt with, what about construction.
It doesn’t matter how good your membrane or technical fabric is if the water can get in elsewhere!
If you look at most high end outerwear garments, you’ll see things like “sealed seams” and “YYK zips”. These matter a lot because seams and zips are weak points in the shell of the garment so making them water tight is pretty big deal.
Lots of ski and snowboard outerwear has flaps over the pockets and zips to keep them from being directly exposed to snow or water. While this works if you’re always upright they don’t always work if you fall a lot or decide to ride in deeper snow.
Water resistant zips and flaps covering vents for weather sealing.
Choosing ski and snowboard outerwear based on the above factors will help you make an informed decision when it comes time to hand over hard earned cash. But, most importantly, choose the garments that fit the purpose you’re looking for. Days of resort riding may prioritise insulation over breathability while backcountry tours may prioritise the highest ratings but work best when combined with layered clothing.
And a final point – Buy For Quality.
These items can be expensive but buying a good quality item with a longer lifespan is better for your wallet and the environment! Keep the garments clean and make sure to use the recommended re-waterproofing solution and you’ll have many happy seasons before you need to think of replacing it!
We've got tons of options for outerwear here and our team have carefully selected each item